Several methods have been known for producing 2,4,5-trifluorobenzoic acid from 2,4,5-trifluorobromobenzene, such as synthesis by Grignard reactions as described, for example, in JP-A-58-188839 (The term "JP-A" as used herein means an "unexamined published Japanese patent application") and synthesis by reaction with cuprous cyanide as described, for example, in JP-A-60-72885, but these methods suffer disadvantages such as difficulty involved in obtaining 2,4,5-trifluorobromobenzene as a starting material.
Many reactions have also been known for dehalogenating aromatic halogen compounds with reducing agents and they include, for example, reduction with triethylsilane in the presence of palladium on carbon as described in J. Org. Chem., 34, G38 (1969), reduction with a zinc/acetic acid system as described in Organic Synthesis, Coll. Vol. 5, p.149 (1973), reduction with a copper/benzoic acid system as described in J. Amer. Chem. Soc., 75, 3602 (1953), and reduction with a triethylsilane/cyclohexane system under ultraviolet irradiation as described in Synthesis, 1971, 537. However, the process of the present invention is not disclosed in any of the known documents including those listed above. The major problem with the prior art methods concerns the need to selectively reduce the 4-position only of tetrafluoroisophthalonitrile which contains four possible sites of dehalogenation (defluorination). It should also be mentioned that 2,4,5-trifluoroisophthalonitrile and 2,4,5-trifluoroisophthalic acid are novel compounds and processes for producing them are of course not yet to be known.